Air knife inlet and exhaust for additive manufacturing

ABSTRACT

An additive manufacturing apparatus includes a platform, a dispenser configured to deliver a plurality of successive layers of feed material onto the platform, at least one energy source to selectively fuse feed material in a layer on the platform, and an air knife assembly. 
     The air knife assembly includes an inlet unit to deliver gas over the platform and an exhaust unit to receive gas from over the platform. The exhaust unit includes a plenum having a port connected to a gas return conduit, and a gas collector that is open at a front end to receive gas from over the platform and has a concave plate at a back end of the gas collector. An aperture is formed at a back of the concave plate between the gas collector and the plenum to provide a constricted flow path for gas from the collector to the plenum.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims the benefitof priority to U.S. application Ser. No. 16/684,524, filed on Nov. 14,2019, the contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This disclosure relates to an air knife system for additivemanufacturing, also known as 3D printing.

BACKGROUND

Additive manufacturing (AM), also known as solid freeform fabrication or3D printing, refers to a manufacturing process where three-dimensionalobjects are built up from successive dispensing of raw material (e.g.,powders, liquids, suspensions, or molten solids) into two-dimensionallayers. In contrast, traditional machining techniques involvesubtractive processes in which objects are cut out from a stock material(e.g., a block of wood, plastic, composite, or metal).

A variety of additive processes can be used in additive manufacturing.Some methods melt or soften material to produce layers, e.g., selectivelaser melting (SLM) or direct metal laser sintering (DMLS), selectivelaser sintering (SLS), or fused deposition modeling (FDM), while otherscure liquid materials using different technologies, e.g.,stereolithography (SLA). These processes can differ in the way layersare formed to create the finished objects and in the materials that arecompatible for use in the processes.

In some forms of additive manufacturing, a powder is placed on aplatform and a laser beam traces a pattern onto the powder to fuse thepowder together to form a shape. Once the shape is formed, the platformis lowered and a new layer of powder is added. The process is repeateduntil a part is fully formed.

SUMMARY

In one aspect, an additive manufacturing apparatus includes a platform,a dispenser configured to deliver a plurality of successive layers offeed material onto the platform, at least one energy source toselectively fuse feed material in a layer on the platform, and an airknife assembly. The air knife assembly includes an inlet unit to delivergas over the platform and an exhaust unit to receive gas from over theplatform. The inlet unit includes a multi-chamber plenum, a gas inlet,and a gas distribution module. The multi-chamber plenum has a pluralityof vertically stacked chambers that are fluidically connected, with afirst chamber of the plurality of vertically stacked chambers positionedat a higher elevation than a collection chamber of the plurality ofvertically stacked chambers. The gas inlet is configured to supply gasinto the first chamber of the plurality of vertically stacked chambers,and the plurality of vertically stacked chambers are configured to guidethe gas from the gas inlet to the collection chamber. The gasdistribution module is fluidically coupled to the collection chamber andincludes at least one perforated sheet positioned for the gas to flowout of the collection chamber through perforations of the at least oneperforated sheet and over the platform.

Implementations may include one or more of the following features.

The gas distribution module may include a plurality of parallelperforated sheets arranged in series along the direction of gas flow.The plurality of parallel perforated sheets may have successivelysmaller apertures. The plurality of parallel perforated sheets may havesuccessively percentage area that is perforated. Each perforated sheetof the at least one perforated sheet may have a length substantiallyequal to a length of the collection chamber.

The collection chamber may have a longitudinally horizontal wall, thewall defining a plurality of nozzles with fluid outlets facing the gasdistribution module. The gas distribution module may have, between thefluid outlets of the nozzles and a first perforated sheet of theplurality of perforated sheets, a plurality of plenums, each plenum ofthe plurality of plenums configured to receive gas from a respectivenozzle of the plurality of nozzles to increase a pressure of the gas inthe respective plenum as gas leaves the respective plenum through arespective portion of the first perforated sheet.

The plurality of vertically stacked chambers may be fluidicallyconnected by a plurality of apertures positioned to form a circuitousflow path for the gas between the first chamber and the collectionchamber. The apertures may span the longitudinal length of the chambers.The plurality of vertically stacked chambers may form an S-shape crosssection, and wherein each chamber of the plurality of vertically stackedchambers may be a longitudinally horizontal chamber. The gasdistribution module may be configured to discharge the gas in a laminarflow parallel to a top surface of the platform.

In another aspect, an additive manufacturing apparatus includes aplatform, a dispenser configured to deliver a plurality of successivelayers of feed material onto the platform, at least one energy source toselectively fuse feed material in a layer on the platform, and an airknife assembly including an inlet unit to deliver gas over the platformand an exhaust unit. The exhaust unit includes a plenum having a portconnected to a gas return conduit, and a gas collector that is open at afront end to receive gas from over the platform and has a concave plateat a back end of the gas collector. An aperture formed at a back of theconcave plate between the gas collector and the plenum provides aconstricted flow path for gas from the collector to the plenum.

Implementations may include one or more of the following features.

The aperture formed at the back of the concave plate may be alongitudinally horizontal slot. The longitudinally horizontal slot mayhave a height of between 9 millimeters and 11 millimeters. Thelongitudinally horizontal slot may extend across a width of the gascollector.

The concave plate may be arranged to deflect the gas from over theplatform toward the aperture. The gas collector may include a ramp plateat a front end of the concave plate. The ramp plate may have a low endadjacent a top surface of the platform such that the ramp plate deflectsthe gas from over the platform upwardly with respect to the platform, toform a residual collection pit at a base of the plenum. The port of theexhaust unit may be disposed at a first lateral side of the plenum and asecond port may be disposed on a second lateral side of the plenum,opposite the first lateral side.

The exhaust unit may have a heat shield plate disposed underneath thegas collector and the plenum. The heat shield plate may be configured toshield the exhaust unit from heat generated at the platform.

Particular implementations of the subject matter described in thisdisclosure can be implemented so as to realize, but are not limited to,one or more of the following advantages.

The air knife assembly can extend and retract smoothly along a linearpath to cover different regions of the build plate. The air knifeassembly can be retracted to allow the dispenser to deliver feedmaterial over the entire build platform. The air knife assembly can alsobe retracted into a sealed compartment so that the components of the airknife are not present during delivery of powder onto the build plate,thus reducing the likelihood of contamination of the air knife.

Gas can flow across a powder bed at a speed that is uniform both acrossthe build plate or platform and along the z-axis perpendicular to thebuild plate. Gas can flow at a uniform speed across a width of about1000 millimeters to cover a large area or an entire width of theplatform. The vertical arrangement of the air knife assembly canincrease the uniformity of the delivered gas over the platform whilereducing the horizontal footprint of the air knife assembly. The gas canhave a flow velocity sufficient, e.g., 1 m/s to 5 m/s, to carry awayspatter induced by metal vapor. This can reduce undesirable inclusionsin the part being fabricated and improve performance of the part.

The details of one or more implementations are set forth in theaccompanying drawings and the description. Other features, aspects, andadvantages of the subject matter will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of an example additive manufacturingapparatus.

FIGS. 2A and 2B are schematic side and top views of a printhead from theadditive manufacturing apparatus.

FIG. 3A is a schematic perspective view, partially cross-sectional, ofthe additive manufacturing apparatus.

FIG. 3B is a schematic cross-sectional front view of a portion of theadditive manufacturing apparatus from FIG. 3A.

FIGS. 4A and 4B are schematic perspective views of an air knife unit andan air knife moving assembly of the additive manufacturing apparatus,showing a supply and return flow path, respectively, of the air knifemoving assembly.

FIG. 4C is a schematic perspective view of the air knife unit and theair knife moving assembly showing a blower connected to supply andreturn conduits of the air knife moving assembly.

FIG. 4D is a block diagram of the supply and return flow paths of theair knife moving assembly.

FIGS. 5A and 5B are schematic top views of the air knife unit and airknife moving assembly, showing the air knife moving assembly inretracted and extended positions, respectively.

FIG. 6A is a schematic perspective view, partially cross-sectional, of aportion of the air knife unit.

FIG. 6B is a detail view of the portion of the air knife unit, takenalong line 6B—6B in FIG. 6A.

FIG. 7 is a schematic side view of the portion of the air knife unit ofFIG. 6A.

FIG. 8 is a schematic perspective view, partially cross-sectional, ofthe air knife unit.

FIG. 9 is a schematic perspective view, partially cross-sectional, of aportion of the air knife unit showing nozzles of the portion of the airknife unit.

FIG. 10 is a schematic perspective view, partially cross-sectional, of adifferent portion of the air knife unit.

FIG. 11 is a schematic side view of the portion of the air knife unit ofFIG. 10.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

In many additive manufacturing processes, energy is selectivelydelivered to a layer of feed material, e.g., powder, dispensed by theadditive manufacturing apparatus to fuse the feed material in a pattern,thereby forming a portion of an object. For example, a light beam, e.g.,a laser beam, can be reflected off a galvo scanner or a rotating polygonscanner to drive the light beam in a path across the layer of feedmaterial. During this fusing process, vapor can be generated as thepowder is fused. For example, where the feed material is a metal powder,vapor trapped in the metal powder can be released when the metal ismelted. In addition, a portion of the liquid metal itself could bevaporized. This vapor can generate spatter. For example, liquid portionsof the molten pool of metal can be ejected when the vapor boils out ofthe metal, powder particles can similarly be blown from the layer ofpowder by the vapor escaping from the liquid metal, and vaporized metalcan precipitate to form a liquid. At the ‘interaction zone’ where thelaser beam interacts with the metal powder, the ‘recoil pressure’ caninduce high velocity ‘melt-flow’ ejection from the interaction zone.Consequently, some powder particles can get enough energy to be blownoff from the powder layer (on the build platform). When these ‘air bornepowder particles’ intersect with the laser-beam path, they burnspontaneously (because laser beam energy for singular particles is highenough to burn them) to form a burnt debris. This spatter cancontaminate surrounding regions of the part (e.g., the fused metalpowder layer), resulting in undesirable inclusions, which can negativelyimpact the performance of the object.

A technique to reduce spatter is to use an “air knife” to blow the vaporand/or spatter away from the layer, thus reducing the likelihood ofcontamination. One of the major requirements of an air-knife is to beefficient in removing these burnt debris from the freshly fused metalpowder layer. However, any non-uniformity in the air flow from the knifecan result in inefficient spatter mitigation. An air knife having someor all of the features described below can provide improved uniformityof air flow across the build plate.

Another issue is that the air knife can occupy space needed for otheroperations, e.g., depositing powder onto the bed. Moreover, when powderis being delivered onto the bed, there is some risk that small amountsof powder can stick to other surfaces in the chamber. By retracting theair knife into a sealed chamber, space is freed up for other componentsand the risk of contamination of the air knife is reduced.

Another issue is that production of high quality parts may occur insidea housing or chamber of limited space. Thus, construction of an additivemanufacturing system having an air knife assembly with a reducedfootprint can allow the additive manufacturing system to use a largeportion of the platform area for part production.

Additive Manufacturing Apparatus

FIG. 1 illustrates a schematic side view of an example additivemanufacturing (AM) apparatus 100 that includes an air knife assembly orunit 200, a printhead 102, and a build platform 104 (e.g., a buildstage). The printhead 102 dispenses layers of one or more powders on atop surface 105 of the platform 104. By repeatedly dispensing and fusinglayers of powder, the apparatus 100 can form a part on the platform.

The air knife assembly 200, the printhead 102, and the build platform104 can both be enclosed in a housing 130 that forms a sealed centralchamber 136 that provides a controlled operating environment, e.g., avacuum chamber. For example, the central chamber 136 can be vacuumed outto bring down the oxygen concentration to less than 1% of the air tothen add an inert gas inside the chamber 136 to maintain a low level ofcontaminants and unnecessary gas concentrations. The inert gas can beused by the air knife assembly 200 to form a laminar curtain above thebuild platform.

The housing 130 can also include an air knife storage chamber 248, e.g.,a load lock chamber, on one side of the central chamber 136 and aprinthead storage chamber 133 on an opposite side of the central chamber136. In some implementations, the air knife storage chamber 248 and theprinthead storage chamber 133 can be disposed on adjacent perpendicularside walls of the central chamber 136.

The central chamber 136 can include an inlet 132 coupled to a gas sourceand an outlet 134 coupled to an exhaust system, e.g., a pump. The gassource can provide an inert gas, e.g. Ar, or a gas that is non-reactiveat the temperatures reached by the powder for melting or sintering,e.g., N₂. This permits the pressure and oxygen content of the interiorof the housing 130 to be controlled. For example, oxygen gas can bemaintained at a partial pressure below 0.01 atmospheres.

The central chamber 136 may be maintained at atmospheric pressure (butat less than 1% oxygen) to avoid the cost and complexity of building afully vacuum compatible system. Oxygen content can be below 50 ppm whenthe pressure is at 1 atmosphere, e.g., when dealing with Titanium (Ti)powder particles. Because metal powder can be highly reactive(particularly Ti) due to its high surface-area-to-volume ration, oxygenconcentration at less than 1% or less than 50 ppm helps avoid thespontaneous burning of metal powder upon excitation by the laser-beam.Thus, it is imperative to maintain low oxygen concentration and an inertgas environment to reduce the possibility of burning of metal powders.

The air knife assembly 200 is movable by an air knife moving assembly140 that includes a retractable telescopic scissor assembly 149. Theretractable telescopic scissor assembly 149 extends or retracts to movethe air knife assembly 200 laterally across the platform 104. Theplatform can move downward as the additive manufacturing processprogresses. For example, the build platform 104 can move downward by thethickness of one layer after each layer is deposited and fused. Thebuild platform 104 can be vertically movable on a track 139, e.g., arail.

The air knife storage chamber 248 (see FIGS. 4A and 5A) accessiblethrough a valve 138, e.g., a slit valve, can be used to separate thecentral chamber 136 from the air knife storage chamber 248 to isolatethe retracted air knife assembly 200 from the central chamber 136 duringthe deposition of material by the print head 102. The air knife assembly200 can be retracted into and stored in the air knife storage chamber248, which can be sealed off by the slit valve 138. The air knifeassembly 200 can be isolated from the central chamber 136 to remove theprinted piece from the central chamber 136 or to move the printhead 102across the platform 104 to dispose printing material.

The printhead 102 can be retracted into the printhead storage chamber133, which can be sealed off by another slit valve 137, similar to theslit valve 138 of the air knife storage chamber 248. In someimplementations, to remove the printed part from the platform 104, theplatform 104 can be lowered and slid out, with the part still on theplatform 104.

Referring to FIGS. 1 and 2B, the printhead 102 is configured to traversethe platform 104 laterally (shown by arrow A), which can be in the samedirection that the air knife assembly 200 travels during processing ofthe layer. In some implementations, the air knife assembly 200 isretracted into its chamber 248 before using the printhead 102, and viceversa, so that the print head 102 and the air knife assembly 102 do notmove or work over the platform 104 at the same time. For example, theapparatus 100 can include a support, e.g., a linear rail or pair oflinear rails 119, along which the printhead 102 can be moved by a linearactuator and/or motor (not shown). This permits the printhead 102 tomove across the platform 104 along a first horizontal axis. In someimplementations, the printhead 102 can move along a second horizontalaxis perpendicular to the first axis instead of or in addition to movingalong the first axis.

The air knife assembly 200 can move over the platform 104 continuouslyor in discrete steps during the printing process. When the air knifeassembly 200 does not move continuously, the air knife assembly 200 isplaced over a certain region of the platform 104, and after the laserfuses the material over the region, then the air knife assembly 200 canmove to cover a new region of the platform 104.

Referring to FIGS. 1A, 2A and 2B, the platform 104 is movable along avertical axis while the air knife assembly 200 and the printhead 102 aremovable along a horizontal axis. In particular, after each layer ofmaterial 110 is fused to form a portion of the part 10, the platform 104is lowered by an amount equal to the thickness of the deposited layer110 of powder. This can maintain a constant height difference betweenthe dispenser on the printhead 102 and the top of the powder on theplatform 104. A drive mechanism, e.g., a piston or linear actuator, canbe connected to the platform 104 or support holding the platform tocontrol the height of the platform.

As shown in FIGS. 2A and 2B, the printhead 102 includes at least a firstdispenser 112 to selectively dispense a layer 110 of a powder 106 on thebuild platform 104, e.g., directly on the build platform 104 or on apreviously deposited layer. In the implementation illustrated in FIG.2A, the first dispenser 112 includes a hopper 112 a to receive thepowder 106. The powder 106 can travel through a channel 112 b having acontrollable aperture, e.g., a valve, that controls whether the powderis dispensed onto the platform 104. In some implementations, the firstdispenser 112 includes a plurality of independently controllableapertures, so that the powder can be controllably delivered along a lineperpendicular to the direction of travel A.

Optionally, the printhead 102 can include one or more heaters 114 toraise the temperature of the deposited powder. As the printhead 102moves in the forward direction, the heater 114 moves across the areawhere the first dispenser 112 was previously located. The printhead 102can also include one or more spreaders 116, e.g., rollers or blades,that cooperate with the dispensing system 112 to compact and spreadpowder dispensed by the first dispenser 112. In some implementations,the printhead 102 includes a second dispenser 122 to dispense a secondpowder 108 with a smaller mean diameter than the first particles 106,e.g., by a factor of two or more.

In implementations when multiples types of powders are used, the firstand second dispensers 112, 122 can deliver the first and the secondpowder particles 106, 108 each into different selected areas, dependingon the resolution requirement of the portion of the object to be formed.

Examples of metallic particles include metals, alloys and intermetallicalloys. Examples of materials for the metallic particles includetitanium, stainless steel, nickel, cobalt, chromium, vanadium, andvarious alloys or intermetallic alloys of these metals. Examples ofceramic materials include metal oxide, such as ceria, alumina, silica,aluminum nitride, silicon nitride, silicon carbide, or a combination ofthese materials.

In implementations with two different types of powders, in some cases,the first and second powder particles 106, 108 can be formed ofdifferent materials, while, in other cases, the first and second powderparticles 106, 108 have the same material composition. In an example inwhich the apparatus 100 is operated to form a metal object and dispensestwo types of powder, the first and second powder particles 106, 108 canhave compositions that combine to form a metal alloy or intermetallicmaterial.

The processing conditions for additive manufacturing of metals andceramics are significantly different than those for plastics. Forexample, in general, metals and ceramics require significantly higherprocessing temperatures. Thus, 3D printing techniques for plastic maynot be applicable to metal or ceramic processing and equipment may notbe equivalent. However, some techniques described here could beapplicable to polymer powders, e.g. nylon, ABS, polyetheretherketone(PEEK), polyetherketoneketone (PEKK) and polystyrene.

Returning back to FIG. 1, the apparatus 100 also includes at least oneenergy delivery system 150 that can generate at least one light beam 152that is directed toward the uppermost layer of powder on the platform104 and that can be used at least for fusing of the layer of powder onthe platform 104. The light beam 152 and/or another light beam can beused for pre-heating and/or heat-treating the layer of powder.

The air knife assembly 200 generates a flow of gas (shown by arrow 206)across the layer of power. This flow of gas 206 can help reduce spatteror burnt waste caused by fusing of the powder by the light beam 152. Asnoted above, the air knife assembly 200 can translate across the buildplatform 104. The printhead 102 and the air knife assembly 200 areindependently movable. In some implementations, the air knife assembly200 can translate along the same direction (e.g., shown by arrow A) asthe printhead 102. Alternatively, the printhead 102 can translate alonga horizontal direction perpendicular to the direction traveled by theair knife assembly 200.

Referring to FIGS. 1 and 3A, the energy delivery system 150 can includean upper frame 189 to which various components, e.g., components of theenergy delivery system 150, are secured. In some implementations, theupper frame 189 is a portion of the housing 130, e.g., the ceiling ofthe housing 130. A lower frame 141 can surround the build platform 104.This lower frame 141 can be a portion of the housing 130. The upperframe 189 can be secured to the lower frame 141 by a side wall 280,e.g., a side wall of the housing 130. Although FIGS. 1 and 3A illustratethe frames 189 and 141 forming the closed housing, the frames 189 and141 can be configured as an open framework sitting within the housing130.

Referring also to FIG. 3B, the frames 189 and side wall 280 (see FIG. 3)define an open volume 144 that extends from the surface 105 of the buildplatform 104 to the optical components of the energy delivery system150. The open volume 144 at least encompasses a field of view 184 of theenergy delivery system 150, i.e., the region through which the lightbeam(s) 152 can sweep to scan the layer 110 of powder. The air knifeassembly is configured to generate the flow of gas across a portion ofthe open volume 144 that is adjacent the layer 110 on the build platform104.

The energy delivery system 150 includes at least one light source togenerate at least one light beam 152 and at least one reflector assemblyto scan the light beam 152 on the layer 110 of powder.

Referring to FIG. 3B, in some implementations, the energy deliverysystem 150 includes windows 181 defined by apertures at the top of thehousing 130, e.g., apertures in the upper frame 189. The windows 181 canbe formed of quartz or similar transmissive material. The energydelivery system 150 can include a beam scanning system above each window181 at the top of the housing 130. The optical assembly of the beamscanning system can include two galvo mirrors, a polygon, or somethingmore complex.

For example, the energy delivery system 150 includes a first beamscanning system 160, a second beam scanning system 170, and a third beamscanning system 150. The three beam scanning systems 160, 170, 150generate three light beams 162, 172, 152, respectively, that are scannedon the layer 110 of powder. Each beam scanning system 150, 160, and 170can include an optical assembly that could include dual galvo mirrors186, or a polygonal mirror scanner, in order to drive the light beam ina path across the layer 110 of powder. Each beam scanning system canalso include various focusing optics. Each beam scanning system 160,170, 150 can be secured to the frame 189 (see FIG. 1).

The scanning systems 150, 160, and 170 can include a light source 188,e.g., a laser, to generate a light beam, e.g., a laser beam. The lightsource 188 can be a light-emitting diode, e.g., a 400-450 nm blue lightemitting diode, a laser, e.g., a 500-540 nm second harmonic laser, oranother appropriate light source.

In some implementations, the field 184 of the first light beam 152 andthe field of the second and third beams each cover the entire width ofthe build area on the platform 104.

The various beam scanners 160, 170, 150 can each be used for pre-heatingof the powder, fusing of the powder, and/or heat treatment of the layer.In the case of pre-heating, a light beam raises the temperature of thepowder from an initial temperature to an elevated temperature that isstill below the temperature at which the powder melts or fuses. In thecase of fusing, a light beam scans the layer of powder and selectivelyraises the temperature of the powder to a temperature sufficient for thepowder to melt or fuse. In the case of heating-treatment, a light beamdelivers heat so as to control the rate of cool down of the material.

As shown in FIGS. 1 and 3A, the air knife assembly 200 has an inlet unitor module 202 and an exhaust unit or module 204 that work in tandem toremove vapor and spatter from the volume above the platform with a gasreceived from the air knife assembly 200.

The retractable telescopic scissor assembly 149 of the air knife movingassembly 140 has a first arm assembly 262 and a second arm assembly 263that each rotate inward or outward to extend or retract the retractabletelescopic scissor assembly 149. As further described in detail belowwith respect to FIGS. 4A and 4B, the first arm assembly 262 includes asupply conduit 252 and a return conduit or chamber 250 (e.g., theinterior of each arm), with the supply conduit 252 disposed inside thereturn chamber 250, and the second arm assembly 263 includes a secondsupply conduit 256 and a second return chamber 254. The second supplyconduit 256 and second return chamber 254 are similar to the supplyconduit and return chamber of the first arm assembly 262. The supplyconduits and return chambers of the retractable telescopic scissorassembly 149 are fluidically connected to the air knife assembly 200 tosupply gas and receive gas from the air knife assembly 200,respectively.

Referring to FIGS. 4A and 4B, the air knife moving assembly 140 movesthe air knife assembly 200 and includes fluid conduits to supply gas tothe air knife assembly 200. The air knife moving assembly 140 isrotatably coupled to the air knife assembly 200 to move the air knifeassembly 200 along or across a surface of the platform 104. For example,the retractable telescopic scissor assembly 149 of the air knife movingassembly 140 has a first pair of arms 260 and 261 each having a firstend rotatably coupled to a stationary portion (for example, the airknife storage chamber 248), and a second pair of arms 264 and 265 eachhaving a second end 276 and 277 rotatably coupled to the air knifeassembly 200. The first pair of arms 260 and 261 are coupled torespective actuators 312 (e.g., electric motors) that pivot or rotatethe first pair of arms 260 and 261 to extend or retract the retractabletelescopic scissor assembly 149.

A third pair of arms 262 and 263 can be used to connect the first pairof arms 260, 261 to the second pair of arms 264, 265. For example, thefirst ends of the third pair of arms 264, 265 can be coupled to thesecond ends of the first pair of arms 261, 262, and the second ends ofthe third pair of arms 264, 265 can be coupled to the first ends of thesecond pair of arms 261, 262. However, other configurations are possiblefor a scissors telescopic scissor assembly.

Referring to FIGS. 5A and 5B, each arm of the first pair of arms 260 and261 is rotatably coupled to and movable by their respective actuator 312at the load lock chamber 240. The pair of arms 260 and 261 can rotate,upon being actuated by their respective actuator 312, inwardly oroutwardly to extend or retract the retractable telescopic scissorassembly 149. The apparatus 100 also includes a guide rail 119 thatguides or constrains the air knife assembly 200 to move parallel to thesurface of the platform 104 in a generally straight line as theretractable telescopic scissor assembly 149 retracts or extends to movethe air knife assembly 200. The air knife moving assembly 140 can movethe air knife assembly 200 from a first position (see FIG. 5A) removedfrom the platform 104 to a second position (see FIG. 5B) on top of andat a far end of the platform 104.

Referring back to FIG. 4A the retractable telescopic scissor assembly149 provides gas to the air knife assembly 200 through the first gassupply conduit 252 and the second gas supply conduit 256. Referring toFIG. 4B, the retractable telescopic scissor assembly 149 receives thereturn gas from the air knife assembly 200 through the first gas returnchamber 250 (e.g., the hollow interior of the arms) and the second gasreturn chamber 254.

Referring also to FIGS. 4C and 4D, the supply conduits 252 and 256 arefluidically connected to an outlet of a blower 289 and the returnchambers 250 and 254 are fluidically connected to an inlet of the blower289. For example, the supply conduits 252 and 256 can each be connectedto respective supply hoses or conduits 282 and 286 that are fluidicallyconnected to a first manifold 303 fluidically connected to the outlet ofthe blower 289. In some implementations, the supply conduits 252 and 256of the retractable telescopic scissor assembly 149 can be directlycoupled to the first manifold 303. Similarly, the return chambers 250and 254 can be fluidically coupled to respective return hoses orconduits 281 and 284 that are fluidically connected to a second manifold301 fluidically connected to the inlet of the blower 289. The secondmanifold 301 can be fluidically connected to a filter 288 that preventssome particles from entering the blower 289.

The blower 289 is configured to flow gas through the supply and returnconduits at substantially equal rates. For example, the blower 289 canblow (or exhausts) about 3800 liters per minute to maintain about 93%velocity or pressure uniformity across the platform 104.

Referring to FIG. 4A, each supply conduit 252 and 256 extendscontinuously along respective arms 262 and 263 of the retractabletelescopic scissor assembly 149. For example, as described earlier withrespect to FIG. 3A, the retractable telescopic scissor assembly 149 hasa first arm assembly 262 and a second arm assembly 263. The first armassembly 262 has three arms rotatably connected to one another. Thefirst arm assembly 262 has a first arm 260, a second, middle arm 268,and a third arm 264. The first arm 260 is rotatably connected, at afirst end to the air knife storage chamber 248 and rotatably connected,at a second, opposite end to the middle arm 268. The middle arm is 268is rotatably connected to the first arm 260 at a first end and to thethird arm 264 at a second, opposite end of the middle arm 268. The thirdarm 264 is rotatably connected to the middle arm 268 at a first end androtatably connected to the air knife assembly 200 at a second, oppositeend of the third arm 264. The second arm assembly 263 is similar to thefirst arm assembly 262, with three arms rotatably connected to eachother. The middle arm 268 of the first arm assembly is rotatablyconnected, at a middle point of the arm, to a middle arm 269 of thesecond arm assembly 263. The gas supply conduits 252 and 256 extendcontinuously along the length and joints 259 (e.g., rotary pneumaticjoints) of the arm assemblies 262 and 263. The return gas flowscontinuously around and exterior surface of supply conduits 252 and 256,inside each arm of the retractable telescopic scissor assembly 149.

The supply conduits 252 and 256 of the retractable telescopic scissorassembly 149 are both fluidically connected to respective third fluidsupply conduits 292 of the air knife assembly 200. The supply conduits292 of the air knife assembly 200 fluidically connect the inlet unit 202of the air knife assembly 200 to the gas supply conduits 252 and 256 ofthe retractable telescopic scissor assembly 149. Specifically, the thirdsupply conduits 292 are fluidically coupled to respective supplyconduits 252 and 256 of the retractable telescopic scissor assembly 149to receive the gas from the supply conduits 252 and 256. One of thethird supply conduits 292 delivers gas to the inlet unit 202 at a first,lateral end of the inlet unit 202, and another one of the third supplyconduits 292 delivers gas to the inlet unit 202 at a second, lateral endof the inlet unit 202 opposite the first lateral end.

Referring to FIG. 4B, the gas return chambers 250 and 254 arefluidically connected to the exhaust unit 204 of the air knife assembly200. The gas return chambers 250 and 254 of the retractable telescopicscissor assembly 149 are both fluidically connected to respective thirdfluid return conduits 290 of the air knife assembly 200. The returnconduits 290 of the air knife assembly 200 fluidically connect theexhaust unit 204 of the air knife assembly 200 to the gas returnchambers 250 and 254 of the retractable telescopic scissor assembly 149.Specifically, the third return conduits 290 are fluidically coupled torespective return chambers 250 and 254 of the retractable telescopicscissor assembly 149 to flow the gas from the exhaust unit 204 to thereturn chambers 250 and 254. One of the third supply conduits 290receives gas from the exhaust unit 204 at a first, lateral end of theexhaust unit 204, and another one of the third return conduits 290receives gas from the exhaust unit 204 at a second, lateral end of theexhaust unit 204, opposite the first lateral end.

Referring back to FIGS. 1 and 3A, the inlet unit 202 and the exhaustunit 204 of the air knife assembly 200 are positioned on opposite sidesof the air knife assembly 200, with the exhaust unit 204 spaced apartfrom and facing the inlet unit 202. The inlet unit 202 supplies the gasfrom the gas blowers 244 and 242 (see FIG. 4A) over the platform surface105 to remove burn waste and be received by the exhaust unit 204, whichin turn sends the received gas from over the platform 104 back to thegas blowers 244 and 242.

Referring to FIG. 6A, the gas inlet unit 202 has a multi-chamber plenum270 that has multiple vertically stacked chambers 271, 272, 273, and 402that are fluidically connected. The first chamber 271 of the pluralityof vertically stacked chambers is positioned at a higher elevationvertically than the last chamber (for example, a collection chamber) 402of the plurality of vertically stacked chambers. The vertically stackedchambers 271, 272, 273, and 402 are fluidically connected by respectiveapertures 271 a, 272 a, and 273 a positioned to form a circuitous flowpath 302 for the gas between the first chamber 271 and the collectionchamber 402. The apertures 271 a, 272 a, and 273 a can span thelongitudinal length of the chambers 271, 272, 273, and 402.Alternatively, each single aperture can be replaced by multiple discretespaced apart holes. The chambers 271, 272, 273, and 402 span thelongitudinal length of the inlet unit 202. The multiple verticallystacked chambers 271, 272, 273, and 402 are longitudinally horizontalchambers that, looking from a side, form a flow path for the gas thathas multiple reversals in direction, e.g., an S-shape cross section.

The inlet unit 202 also has a gas distribution module 406 fluidicallycoupled to the collection chamber 402. The gas distribution module 406has multiple perforated sheets 410, 412, and 414 positioned for the gasto flow out of the collection chamber 402, through perforations of theperforated sheets 410, 412, and 414 and over the platform 104. The inletunit 202 also has a heat shield plate 444 disposed underneath thecollection chamber 402 and the gas distribution module 404. The heatshield plate 444 shields the inlet unit 202 from heat generated at theplatform 104, e.g., from the heated powder.

Referring also to FIG. 7, the inlet unit 202 also includes a gas inlet502 configured to supply gas into the first chamber 271 of the pluralityof vertically stacked chambers 271, 272, 273, and 402. The gas inlet 502is fluidically connected to the third supply conduit 292 of the airknife assembly 200. The gas inlet can be in the side wall so that thegas enters the uppermost chamber 271 in a direction perpendicular to theeventual gas flow 206 from the distribution module 406. The verticalconfiguration of the chambers increases the distance traveled by thegas, while reducing the horizontal footprint of the inlet unit 202. Thelonger the distance traveled by the gas, the more uniform is thepressure and velocity of the gas. The inlet unit 202 has a height ‘h’ ofabout 170 millimeters and a thickness ‘t’ of about 120 millimeters.

The chambers 271, 272, 273, and 402 guide the gas from the gas inlet 502to the collection chamber 402, to be derived from the collection chamberto the gas distribution module 406. The gas leaves the gas distributionmodule 406 to flow along a portion 146 of the open volume that isadjacent the material layer on the build platform 104. The portion 146can include a height of about 20 to 30 millimeters. In other words, thegas leaves the inlet unit 202 to form a gas curtain with a height ofabout 20 to 30 millimeters. The gas distribution module 406 dischargesthe gas in a laminar flow parallel to the top surface of the platform104.

Referring to FIG. 6B, the gas distribution module 406 includes multiplehorizontally longitudinal housings defined between the three perforatedsheets 410, 412, and 414. The three perforated sheets 410, 412, and 414can be arranged in parallel and spaced apart along the direction of gasflow 206 across the platform. The perforated sheets 410, 412, and 414have apertures that decrease in size along the flow direction of thegas, with the first sheet (e.g., the upstream sheet) 410 having thelargest apertures. For example, the first perforated sheet 410 definesfirst apertures 420, the second, middle perforated sheet 412 definessecond apertures 422 smaller than the first apertures 420, and the thirdperforated sheet 414 defines third apertures 424 smaller than the secondapertures 422. The second sheet 412 is disposed between the first sheet410 and the third sheet 414. The first perforated sheet 410 can have aperforated area of about 30-40% of the area of the sheet to let the gaspass through, the second perforated sheet 412 can have a perforated areaof about 25-30% to let gas pass through, and the third perforated sheetcan have a perforated area of about 20-25% to let gas pass through. Theair accumulation in each space or housing between the sheets 410, 412,and 414 can even out the gas pressure to deliver, at the last sheet 414,a laminar flow of gas with generally uniform pressure and velocity. Eachperforated sheet 410, 412, and 414 has a horizontal length (for example,a width) substantially equal to a length of the collection chamber 402.

Referring to FIGS. 7 and 8, the collection chamber 402 has alongitudinally horizontal wall 499 that defines multiple nozzles 404that converge in the direction of the gas flow, with fluid outletsfacing the gas distribution module 406. The wall 499 of the collectionchamber 402 can have 12 nozzles 404 distributed evenly along a width ‘w’of the wall 499. The width ‘w’ of the wall can be about 1000millimeters. Each convolution of the multi-chamber plenum 270distributes the gas (for example, reduces the turbulence of the gas),and the nozzles 404 help redistribute the volume of gas even further toincrease the uniformity of the gas flow.

Referring to FIG. 9, the gas distribution module 406 has, between thefluid outlets 405 of the nozzles 404 and the first perforated sheet 410,multiple plenums 602. The plenums 602 are defined between partitions 601that define spaces of generally equal longitudinal length. The plenums602 can be evenly distributed along the width of the gas distributionmodule 406, with each plenum 602 being associated with a respectivenozzle 404. For example, if there are twelve nozzles 404, there can betwelve plenums 602. Each plenum 602 receives gas from a respectivenozzle 404 to increase the pressure of the gas in the respective plenum602 as gas accumulates and then leaves the respective plenum 602 througha respective portion of the first perforated sheet 410.

Referring to FIGS. 10 and 11, the exhaust unit 204 of the air knifeassembly 200 has a plenum 603 with a port 610 connected to the gasreturn conduit 290 of the air knife assembly 200. As shown in FIG. 10,the port 610 of the exhaust unit 204 is disposed at a first lateral sideof the plenum 603, and a second port is disposed at a second lateralside of the plenum 603, opposite the first lateral side. Additionally,the exhaust unit 204 has a gas collector 601 that includes a concaveplate 612, a ramp plate 614, and a portion of a base plate 613 of theexhaust unit 204. The gas collector 601 is open at a front end toreceive gas 206 from over the platform. The concave plate 612 isdisposed at a back end of the gas collector 601. The exhaust unit 204defines an aperture 618 formed at a back of the concave plate 612,between the gas collector 601 and the plenum 603 that provides aconstricted flow path for gas 206 from the collector 601 to the plenum603.

The aperture 618 can be a longitudinally horizontal slot. Thelongitudinally horizontal slot can have a height of between 9millimeters and 11 millimeters. The optimal height of the slot dependson the velocity of the gas flowing over the platform 104. Thelongitudinally horizontal slot extends across a width of the gascollector 601.

The concave plate 612 is arranged to deflect the gas from over theplatform 104 toward the aperture 618. For example, the curvature of theconcave plate 612 has a radius that deflects the gas downward and towardthe aperture 618, instead of reflecting the gas back to the platform104.

The ramp plate 614 of the gas collector 601 is disposed at a front endor in front of the concave plate 612. The ramp plate 614 has a low end631 adjacent the top surface 105 of the platform 104 such that the rampplate 614 deflects the gas from over the platform 104 upwardly withrespect to the platform 104, to form a residual collection pit 620 atthe base of the plenum 603. The residual collection pit 620 captures theparticles from over the platform 104 so the particles don't return tothe blowers and then to the platform 104. For example, light debriswould be taken out through exhaust, but heavier particles can settle inthe collection pit 620.

The exhaust unit 204 also has a heat shield plate 616 disposedunderneath the gas collector 601 and the plenum 603 to shield theexhaust unit 204 from heat generated at the platform 104.

The air knife assembly 200 can deliver flow velocities of 2-3 m/s. Thegas can be an inert gas, e.g., Argon. Such velocity ensures thatparticles or burnt waste is removed from the platform 104.

Referring back to FIG. 1, the apparatus 100 includes a controller 195coupled to the various components of the apparatus, e.g., power sourcesfor the light sources and heaters, actuators and/or motors to move theair knife moving assembly 140, actuators and/or motors for thecomponents, e.g., dispensers and beam scanners, within the printhead102, to cause the apparatus to perform the necessary operations tofabricate an object.

The controller 195 can include a computer aided design (CAD) system thatreceives and/or generates CAD data. The CAD data is indicative of theobject to be formed, and, as described herein, can be used to determineproperties of the structures formed during additive manufacturingprocesses. Based on the CAD data, the controller 195 can generateinstructions usable by each of the systems operable with the controller195, for example, to dispense the powder 106, to fuse the powder 106, tomove various systems of the apparatus 100, and to sense properties ofthe systems, powder, and/or the object 10. In some implementations, thecontroller 195 can control the first and second dispensing systems 112,122 to selectively deliver the first and the second powder particles106, 108 to different regions.

The controller 195, for example, can transmit control signals to drivemechanisms that move various components of the apparatus. In someimplementations, the drive mechanisms can cause translation and/orrotation of these different systems, including. Each of the drivemechanisms can include one or more actuators, linkages, and othermechanical or electromechanical parts to enable movement of thecomponents of the apparatus.

CONCLUSION

The controller and other computing devices part of systems describedherein can be implemented in digital electronic circuitry, or incomputer software, firmware, or hardware. For example, the controllercan include a processor to execute a computer program as stored in acomputer program product, e.g., in a non-transitory machine readablestorage medium. Such a computer program (also known as a program,software, software application, or code) can be written in any form ofprogramming language, including compiled or interpreted languages, andit can be deployed in any form, including as a standalone program or asa module, component, subroutine, or other unit suitable for use in acomputing environment.

While this document contains many specific implementation details, theseshould not be construed as limitations on the scope of any inventions orof what may be claimed, but rather as descriptions of features specificto particular embodiments of particular inventions. Certain featuresthat are described in this document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. For example:

-   -   Other techniques can be used for dispensing the powder. For        example, powder could be dispensed in a carrier fluid, e.g., a        quickly evaporating liquid such as Isopropyl Alcohol (IPA),        ethanol, or N-Methyl-2-pyrrolidone (NMP), and/or ejected from a        piezoelectric printhead. Alternatively, the powder could be        pushed by a blade from a powder reservoir adjacent the build        platform.    -   Although FIG. 3B illustrates three galvo scanners, the system        could have a larger or smaller number of each kind of scanner,        and could also include polygon scanners. For example, the system        could include just a single polygon scanner, just a single galvo        scanner, just two polygon scanners, just two galvo scanners, or        a single polygon scanner and a single galvo scanner, two each of        galvo and polygon scanners, etc. Any given scanner could be used        for pre-heating and/or heat treatment and/or fusing of the        powder.    -   For some powders, an electron beam could be used instead of a        laser beam to fuse the powder. So the second energy delivery        system could include an electron beam source and electron beam        scanner rather than a light source and pair of galvo mirror        scanners.

Accordingly, other implementations are within the scope of the claims

What is claimed is:
 1. An additive manufacturing apparatus comprising: a platform; a dispenser configured to deliver a plurality of successive layers of feed material onto the platform; at least one energy source to selectively fuse feed material in a layer on the platform; and an air knife assembly including an inlet unit to deliver gas over the platform, and an exhaust unit including a plenum having a port connected to a gas return conduit, and a gas collector that is open at a front end to receive gas from over the platform and has a concave plate at a back end of the gas collector, and wherein an aperture formed at a back of the concave plate between the gas collector and the plenum provides a constricted flow path for gas from the collector to the plenum.
 2. The apparatus of claim 1, wherein the aperture formed at the back of the concave plate comprises a longitudinally horizontal slot.
 3. The apparatus of claim 2, wherein the longitudinally horizontal slot comprises a height of between 9 millimeters and 11 millimeters.
 4. The apparatus of claim 2, wherein the longitudinally horizontal slot extends across a width of the gas collector.
 5. The apparatus of claim 1, wherein the concave plate is arranged to deflect the gas from over the platform toward the aperture.
 6. The apparatus of claim 1, wherein the gas collector comprises a ramp plate at a front end of the gas collector, the ramp plate comprising a low end adjacent a top surface of the platform such that the ramp plate deflects the gas from over the platform upwardly with respect to the platform, to form a residual collection pit at a base of the plenum.
 7. The apparatus of claim 6, wherein a height of the ramp plate is less than a height of the aperture.
 8. The apparatus of claim 6, wherein the base of the plenum comprises a planar floor.
 9. The apparatus of claim 1, wherein the port of the exhaust unit is disposed at a first lateral side of the plenum and a second port is disposed on a second lateral side of the plenum, opposite the first lateral side.
 10. The apparatus of claim 9, comprising return conduits extending vertically from the port and second port.
 11. The apparatus of claim 1, wherein the gas collector comprises a portion extending horizontally toward the inlet unit from an inner edge of the concave plate.
 12. The apparatus of claim 1, wherein the exhaust unit comprises a heat shield plate disposed underneath the gas collector and the plenum, the heat shield plate configured to shield the exhaust unit from heat generated at the platform.
 13. A method of removing burnt waste from a platform of an additive manufacturing apparatus, the additive manufacturing apparatus comprising a platform, a dispenser configured to deliver a plurality of successive layers of feed material onto the platform, at least one energy source to selectively fuse feed material in a layer on the platform, and an air knife assembly including an inlet unit to deliver gas over the platform and an exhaust unit to receive gas from over the platform, the inlet unit comprising a multi- chamber plenum, the multi-chamber plenum comprising a plurality of vertically stacked chambers fluidically connected with a first chamber of the plurality of vertically stacked chambers positioned at a higher elevation than a collection chamber of the plurality of vertically stacked chambers, and a gas distribution module fluidically coupled to the collection chamber, the method comprising: dispensing, by the dispenser, a layer of feed material over the platform; fusing, by the energy source, the feed material, the fusing producing burnt waste over the platform; receiving, by the inlet unit and from a gas supply conduit of the additive manufacturing apparatus, a gas; flowing, by the inlet unit, the gas along the vertically stacked chambers from the first chamber to the collection chamber, and from the collection chamber to the gas distribution module; flowing, by the inlet unit, a laminar flow of the gas parallel to a top surface of the platform to substantially remove the burnt waste from over the platform; and receiving, by the exhaust unit, the laminar flow from over the platform.
 14. The method of claim 13, wherein the exhaust unit of the air knife assembly includes a plenum having a port connected to a gas return conduit, and a gas collector that is open at a front end to receive the gas from over the platform and has a concave plate at a back end of the gas collector, an aperture formed at a back of the concave plate between the gas collector and the plenum configured to provide a constricted flow path for gas from the collector to the plenum, and wherein receiving the laminar flow comprising deflecting, by the concave plate, the gas to the aperture to be received by the plenum. 